This invention relates to a process for preparing certain Group 4 transition metal complexes possessing neutral diene ligands. The complexes are useful as components or precursors of components in addition polymerization catalysts used in preparing polyolefins, especially crystalline polypropylene.
The preparation and characterization of certain biscyclopentadienyl zirconium and hafnium diene complexes is described in the following references: Yasuda, et al., Organometallics, 1982, 1, 388 (Yasuda I); Yasuda, et al. Acc. Chem. Res., 1985, 18 120 (Yasuda II); Erker, et al., Adv. Organomet. Chem., 1985, 24, 1 (Erker I); Erker et al. Chem. Ber., 1994, 127, 805 (Erker II); and U.S. Pat. No. 5,198,401. Certain of the present metal diene complexes and methods for preparing the same have been previously disclosed in U.S. Pat. Nos. 5,512,693, 5,527,929, and 5,679,816. U.S. Pat. Nos. 5,470,993 and 5,491,246 disclosed monocyclopentadienyl diene complexes with titanium or zirconium in which the metal is in the +2 formal oxidation state. Such metal complexes were formed by contacting a metal complex with a source of the cyclopentadienyl dianion ligand, a reducing agent and the neutral diene compound in any order.
In J. Chem. Soc., Chem. Comm., 24, 1865-1867 (1989) zirconium and hafnium dichloride complexes of 2,3-dimethyl-1-3-butadiene were disclosed. The complexes were also converted to the corresponding non-bridged bis(indenyl) derivatives. In Inorg. Chem, 1981, 20, 1844-1849, complexes of the type [ZrCl.sub.3 (PR.sub.3).sub.2 ].sub.2 which were shown to be chloride bridging dimers, were prepared by reducing ZrCl.sub.4 (PR.sub.3).sub.2 with sodium amalgam.